Expression of different 17 beta-hydroxysteroid dehydrogenase types and their activities in human prostate cancer cells

The 17 beta-hydroxysteroid dehydrogenase (17 beta HSD) enzyme system governs important redox reactions at the C17 position of steroid hormones. Different 17 beta HSD types (no. 1-4) have been identified to date in peripheral human tissues, such as placenta, testis, and breast. However, there is little information on their expression and activity in either normal or malignant prostate. In the present work, we have Inspected pathways of 17 beta-oxidation of either androgen or estrogen in human prostate cancer cells (LNCaP, DU145, and PC3) in relation to the expression of messenger RNAs (mRNAs) for 17 beta HSD types 1-4. These cell systems feature distinct steroid receptor status and response to hormones. We report here that high expression levels of 17 beta HSD4 were consistently observed in all three cell lines, whereas even greater amounts of 17 beta HSD2 mRNA were detected solely in PC3 cells. Neither 17 beta HSD1 nor 17 beta HSD3 mRNAs could be detected in any cell line. From a metabolic standpoint, intact cell analysis showed a much lower extent of 17 beta-oxidation of both androgen [testosterone (T)] and estrogen [estradiol(E-2)] in LNCaP and DU145 cells compared to PC3 cells, where a greater precursor degradation and higher formation rates of oxidized derivatives (respectively, androstenedione and estrone) were observed. Using subcellular fractionation, we have been able to differentiate among 17 beta HSD types 1-4 on the basis of their distinct substrate specificities and subcellular localization. This latter approach gave rise to equivalent results. PC3 cells, in fact, displayed a high level of microsomal activity with a low E-2/T activity ratio and approximately equal apparent K-m values for E-2 and T, suggesting the presence of 17 beta HSD2. Dehydrogenase specific activity with both E-2 and T was also detected, although at lower levels, in LNCaP and DU145 cells. No evidence for reductase activity could be obtained in either the soluble or microsomal fraction of any cell line, As comparable expression levels of 17 beta HSD4 were seen in the three cell lines, 17 beta HSD2 is a likely candidate to account for the predominant oxidative activity in PC3 cells, whereas 17 beta HSD4 may account for the lower extent of E-2 oxidation seen in both LNCaP and DU145 cells. This is the first report on the expression of four different 17 beta HSD types in human prostate cancer cells. It ought to be emphasized that for the first time, analysis of different 17 beta HSD activities in either intact or fractionated cells harmonizes with the expression of relevant mRNAs species.